Electron discharge device



y N0v.26,1940. H MAHL. y 2,223,040

ELECTRON DISCHARGE DEVICE Filed June 25, 1938 P0 TEN 77A LS M A l A INVENTOR.

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Patented Nov. 26, 1940 PATENT OFFICE ELECTRON DISCHARGE DEVICE Hans Mahl, Berlin-Reinickendorf, Germany, assignor to General Electric Company, a corpora tion of New York Application June 25, 1938, Serial No. 215,749

In Germany June 30,v 1937 7 Claims.

This invention relates to electron discharge devices and more particularly, to the methods and means for improvements in producing and operating such devices of the class known as cathode ray tubes.

It is a well known fact that one of the reasons which make the production of intense spots of minimum size inside a high vacuum as required especially in electron-ray tubes such as cathode 10 ray oscillographs or television tubes so difficult, is the laokof adequate electron density of the incandescent cathode employed therefor. The best high emission cathodes such as oxide cathodes have a maximum specific emission of an order of magnitude of 1 amp. per sq. cm. Any substantial increase beyond this limit may not be expected from cathodes of this kind. To overcome this shortcoming, this invention proposes to use cathodes of the so-called auto-electric type wherein emissivity of electrons is brought about by local high electrostatic field intensity. In fact, at such local points, it is feasible to realize current densities of a few thousand amperes per square centimeter. i

Such a cathode in which emissivity is predicated upon the presence and action of local eleotrostatic high field intensitiesmay be used in conjunction with suitable electron-optical means so as to provide spots focused vdown to an extremely small size or area with very intense currents. In order that a well defined punctiform emission may be obtained it is possible to use for the cathode an extremely slender or fine wire point for which, as known, the maximum field intensity arises at the point of minimum curvature. In the presence of proper electron-optical focusing systems, it is feasible to secure a minute punctiform image of emissive surface even where the enlargement is quite sizable, as for example, 10 times, inasmuch as the emissive spot of the pointed cathode is of an order of magnitude of around 10-s sq. cm. But satisfactory electron optical imaging of an auto-electrically emitting point, especially when an electrostatic lens is used, is attended with difficulties insofar as the potentials required at the various electrodes of the electrical lens for focusing introduce problems of providing the necessary field intensity at the cathode. To obtain autoelectric emission 50 a predetermined high electrostatic field intensity is necessary. However, it would be rather diiiicult to make conditions such that the field intensity produced by the lens (which as a general rule is small) will suffice to occasion any appreciable field emission.

(Cl. Z50- 163) According to this invention, in order to produce the requisite high field intensity, areticulate (grate` or lattice) or grid structure or a foil is interposed between the cathode and the electron-optical focusing or imaging system. The 5 use of such grids or foils has been used in connection with a thermionically or a photoelectrically operated cathode. In these arrangements this scheme is intended either to preclude the arising of an electron space-charge or else 10 to secure a substantially homogeneous accelerating field. However, the arrangement here disclosed is entirely different therefrom, since the grid or foil according to this invention is intended to create as highkas possible a field intenl5 sity in front of the cathode under conditions causing as little reduction of the field as a result of grid transparency as possible.

The f oil may beV placed upon ,a reticulate structure, a 1attice, grid, grate, or the like. While 2othe grid or foil, as a general rule may be flat or planar, it is further provided to makey the grid or foil curved so as `to avoid or lessen distortion occasioned by the aberrations of the lens system. I v y 25 Inthe drawing, a number of exemplified embodiments of the means here disclosed are shown by the aid of which theinvention shall be explained in moredetail. At Fig. 1 is schematically an arrangement ofelements in accordance 30T- With the invention; Figs. 2, 3 and 4 show various embodiments o-f the cathode structure in accordance with the invention.. while Figs. 5 and 6 show diagrammatically two detailed embodiments of the invention. Fig. lshows the funda- 35' mentals of the arrangement. Kdenotes the cathode, N is `the grate or grid structure or the foil, L is the electronic lens, and S the luminescent screen of a cathode ray tube.

It is vital and essential in this invention that 40. the cathode be positioned properly with respect to the electron lens system in order that the high concentration of field-,force lines at the cathode shall not distort the fieldforce lines of the electron optical system. If the cathode itself consists of a pointed or tapered slender wire, the disturbing actions occasioned by this point or peak inside the acceleration field must be eliminated to a large extent if electron-optic fok cusing is to be made possible. To avoid such interaction of fields, the point may be set into a disk which may be either planar or curved so that the point protrudes therefrom only to a slight degree, say, .5 millimeter (Fig. 2). Another method of embedding or setting the point thereof While being insulated therefrom. Fig."` i4,

shows a disposition of this nature. D indicates the auto-electrically emissive Wire point (zero potential) St is the control electrode which may f be maintained at a potential of (10i-kv), and G an insulation layer such as a vacuum or a vacuum-stable substance likemica.- To enhance i the eld emission the point or peak is activated by alkali or earth-alkali substances, the latter being applied by vaporization to provide a coat of the desired thickness ory depth.v A particular embodiment of the assembly is shown in Fig. 5. K is the cathode having an auto-electrically emissive peak or point, ANdenotes the reticulate electrode yor grid placed about 1-10 mm. fromthe cathode, kept vat a potential of say 5 kv. in reference to the cathode. 'Ihe electrical lens here consists of several cylindrical electrodes. E1 is the first imaging or focusing cylinder Which may be maintained at a voltage of .3 kv. in reference totthecathode., ,E2 is the second focusing cylinder kept atabout 1 kv. potential. E3 is -the third focusing cylinder maintained at 3 kv. S again denotes the luminescent screen-Which maybe maintained at the same .potential as E3. YFig. 6 shows a corresponding disposition in which theelectrodes E1 and Ezare of the diaphragm type. It Will` be understood that instead of the electrical lenses indicated in the ,exemplified embodiments Figs. 5 and 6, it would be feasible also to mount magnetic lenses or use both kinds simultaneously.

While for purposes of illustration the use of a luminescent screen in vcombination with the cathode and electrode structure has beeny given as an example, it will be understood, of course, that my invention may be used with any' suitabletarget element. v.

Having described my invention WhatI claim is:

f1. A cathode ray tube comprising an envelope vhaving an end Wall, a fluorescent screen mounted on the end Wall, an auto-electric emissivecathode positioned in register with said screen, a field concentrating-distortion reducing reticulate electrode positioned closely adjacent to the cathode and intermediate the cathode and screen, and a plurality of focusingl electrodes intermediate the reticulate electrode and the screen.

2. A cathode ray tube system comprising an envelopehaving an end wall, a iiuorescent screen mounted on the end Wall, an. auto-electric emissive cathode positioned in register with said screen, a curved iield concentrating-distortion reducing reticulate electrode positioned closely adjacent to the cathode and intermediate the cathode and screen, a plurality of focusing electrodes intermediate the curved reticulate electrode and the screen, said reticulate and plurality of electrodes being adapted to be maintained at progressively increasing potential with respect to the cathode.

3. A cathode ray tube comprising a fluorescent screen,`an auto-electric electron emissive cath- 0de, a disk electrode for supporting the cathode, a eld concentrating-distortion reducing reticulate electrode closely adjacent the cathode, said reticulate electrode being adapted to be maintained at a positive potential with respect to said cathode, and a r"plurality of focusing electrodes intermediate the reticulate electrode and the screen. 4

,4. A @cathodev ray tube system comprising a fluorescent screen, an auto-electric electron emissive cathode', a disk electrode for supporting -the cathode, a curved i'leld concentrating-distortion reducing reticulate electrode-closelyadjacent the cathode, a plurality of electrodes intermediate the curved reticulate electrode and the screen, said reticulatenelectrode being adapted to be maintained at a positive potential ,with re-`r spect to the *cathodel `and also beingadapted-to be suppliedl with modulating potentials, andy said plurality of electrodes-being adapted to be -maintained at morev positivey potential With 'respect tothe cathodel than thel reticulate electrode;

5. A cathode ray tube comprising a fluorescent screen, an auto-electric electron emissive cathode, a Vdisk electrode having anun-,like depression therein, means to support said,..cathode .in the cup-like depression of said disk, -a curved Yield.

concentrating-distortion reducing ,reticulate elec-Y trode closely 'adjacent the cathodasai'd reticu-f late electrode being adapted lto be maintained at a positive potentialwithrespect to said cathode, anda plurality of focusing electrodesinterme.- diate the reticulate electrode and th'ezscrjeena M f .6. A cathode ray tube comprising vfa `IuOnescent screen, an apexed lamentary auto-electric electronfemissive cathode, a dislcelectrodev fork supporting said cathode, a' neld `conce'ntratingdistortion reducingl reticulate 'electrode closely adjacent the cathode, said. reticulate elettrode being adapted to be maintained ata positive-potential with respect to said cathode, and y.apinrality of focusing electrodes intermediate the 'reticulate electrode andthe screen.

7. A cathode ray tube comprising a fluorescent screenan auto-electric electron emissive cathode, a disk electrode having ,a cup-like depression therein, means to. support said cathode in the. cup-like depression of saidl disk, a vrcurved field concentrating-distortion reducing reticulate electrode closely adjacent the cathrideV andA adapted to be maintained ata positive, potential with respect to the cathode, said curvedvelectrode having substantially the same curvature ,as the curvature of the cup-like depression in thediskx and. a plurality of focusing electrodes intermediate the reticulate electrode and the screen. I

. Y HANS. `MAI-IL. 

